These studies explore the exchange of water, oxygen, carbon dioxide, carbon monoxide, amino acids and glucose across the placenta and fetal tissues. They include experimental protocols in sheep, rabbits and guinea pigs and the development of mathematical models to describe the complicated interplay of the many processes involved. They include measurement of compliance properties and resistance to blood flow in the fetal liver and umbilical vessels of the placenta. Their long range goal is to identify those factors important for fetal oxygenation and normal growth and development, and hence to the prevention of mental retardation and birth defects.